Does solar scale linearly when you have to get onto roofs to install it? And when each roof is available for installation at different times, so only small crews can do it piecemeal?

It certainly complicates things a bit, but the roofs are independent, so several small teams can independently work in parallel. So yes, it's sort of linear.

Building a large solar installation may scale a bit sub-linearly, if you can e.g. order things in bulk at better prices, and have some electric assemblies done at a factory, more efficiently.